This invention relates to solder glass compositions and methods of using the same for encapsulating integrated circuits or other solid state devices in ceramic packages and it is an object of the invention to provide improved compositions and methods of this nature.
Many integrated circuit devices, or other solid state devices, are encapsulated, or packaged, in ceramic packages consisting of two layers of ceramic material bonded together by a solder glass. Seals of appropriate strength and hermeticity have been found in the past by utilizing relatively high temperatures and solder glasses which devitrified in the sealing process. The devitrification requires a substantial interval of time at the appropriate temperature such for example as 15 minutes at 450.degree.-500.degree.C. It was by devitrification that glasses were produced having the appropriate coefficients of thermal expansion for matching, in effect, those of the ceramic pieces.
In addition to the time of glass sealing, for example, the mounting of the integrated circuit or other solid state device upon a lead frame and that combination upon one of the ceramic layers was time consuming and costly because of the necessary wire bonds which had to be made. The length of time necessary raised the possibility at least of undesirable intermetallic compounds forming, as for example the gold-aluminum intermetallic known as purple plague.
Accordingly it is an object of the invention to provide improved solder glasses and methods of using same for eliminating the disadvantages of the prior art.
It is a further object of the invention to provide improved solder glasses of the nature indicated which are nondevitrifying in nature.
It is a further object of the invention to provide improved solder glasses of the nature indicated which require a greatly reduced period of time for forming a seal with ceramic pieces.
According to the invention strong hermetic seals having appropriate expansion characteristics may be formed in periods of time of less than one minute and at temperatures substantially less than 500.degree.C.